This invention relates to a test device for electrical bonds of semi-conductors, and particularly to a device and method suitable for high speed pull testing.
Electrical bonds of semi-conductor devices often comprise an array of solder or gold balls, on a substrate having electrical pathways. These balls are used to connect individual wires to the pathways, or to connect to pathways of another substrate whilst the substrates are in aligned contact. A solder ball will be re-flowed, and a gold ball will be welded.
Test devices are required to confirm that the balls have sufficient mechanical adhesion to the substrate, in order to confirm viability of the manufacturing technique. It is known to test in shear by driving a tool at the side of a ball, and in tension by gripping and pulling the ball orthogonally to the substrate.
The individual balls are generally arranged in an array, and are very small. A solder ball is typically in the range 1000-75 μm in diameter, whereas a gold ball is in the range 100-20 μm in diameter. These ‘balls’ have a somewhat hemispherical appearance when attached to a substrate. The very small size of some solder and gold balls means that the breaking forces are very low, and special measures are required to reduce friction to a minimum so as to permit breaking force to be measured.
Testing of the ball/substrate bond at a high rate of stress is desirable. In the case of a shear test, the tool can be driven against the respective ball from a distance, and thus the necessary impact speed can be generated. However high speed pull testing of balls is problematic because the test tool must first grip the ball, and thus cannot gather speed or momentum before the test commences.